1. Field of the Invention
The present invention relates to an abnormality detection apparatus of an engine temperature adjusting thermostat for detecting abnormality in operation of the thermostat which serves to open and close a cooling water circulation passage based on a comparison between the temperature of engine cooling water and a predetermined limit temperature, and more specifically it relates to such an abnormality detection apparatus of an engine temperature adjusting thermostat capable of preventing misdetection for improved reliability.
2. Description of the Related Art
In general, an engine is equipped with a cooling system for maintaining the temperature thereof at a proper level with a thermostat being installed for circulating cooling water through a radiator in accordance With the temperature of the engine (i.e., cooling water temperature).
That is, the thermostat operates in such a manner that it closes a cooling water circulation passage thereby to prohibit cooling water from being circulated through the radiator when the temperature of cooling water is lower than a limit temperature, but opens the cooling water circulation passage thereby to allow cooling water to be circulated through the radiator when the temperature of cooling water rises above the limit temperature.
In the past, such a kind of abnormality detection apparatus of an engine temperature adjusting thermostat is disclosed in Japanese Patent Application Laid-Open No. 11-141337 for instance.
FIG. 12 and FIG. 13 are a basic constructional view and a block diagram of essential portions, respectively, of the known abnormality detection apparatus described in the above publication, these figures illustrating the case in which a thermostat abnormality detection apparatus is applied to an engine cooling system of a motor vehicle.
In FIG. 12, an engine 1 having four cylinders includes a piston 4 in each cylinder 3, a crankshaft 5, and a connecting rod 6 connecting a corresponding piston 4 with the crankshaft 5.
The engine 1 further includes a water jacket 7 arranged to surround the cylinders 3, a radiator 8 having an internal space thereof connected to the water jacket 7, a cooling fan 9, a water pump 10, etc.
With the engine 1 as constructed above and illustrated in FIG. 12, an air fuel mixture in a combustion chamber 11 of each cylinder 3 is combusted and exploded to cause a corresponding piston 4 to reciprocate vertically, so that the reciprocating movement of each piston 4 is transmitted to the crankshaft 5 through the associated connecting rod 6 and it is thereby converted into a rotational driving force of the crankshaft 5.
In addition, an air fuel mixture is supplied from an intake pipe to each cylinder 3 through an inlet port (not shown) and combustion gases are discharged therefrom into an exhaust pipe through an exhaust port (not shown).
The water jacket 7 forming a circulation space for cooling water is arranged in such a manner that it surrounds the outer peripheries of the cylinders 3 in order to cool cylinder heads 12 and cylinder blocks 13 heated by the explosion and combustion of the air fuel mixture and maintain them at a constant temperature.
The radiator 8 is in fluid communication with the cooling water circulation passage of the water jacket 7 through an upper connection passage 14 and a lower connection passage 15. A thermostat 16 is provided on the upper connection passage 14.
The thermostat 16 constitutes a valve which mechanically opens and closes according to the temperature TW of engine cooling water For instance, the thermostat 16 becomes a closed state to close the connection passage 14 when the temperature TW of cooling water is 82° C. or less whereas it becomes an open state to open the connection passage 14 when the temperature TW of cooling water exceeds 82° C.
A water temperature sensor 41 provided in an inner wall of the water jacket 7 detects the temperature TW of cooling water and generates a corresponding detection signal to an electronic control unit (ECU) 51.
Now, reference will be made to the electronic control unit (ECU) 51 which performs control and abnormal diagnosis on the thermostat 16 based on the operating conditions of the engine 1 while referring to FIG. 13.
In FIG. 13, the ECU 51 includes a CPU 52, a ROM 53, a RAM 54, a backup RAM 55, a timer counter 56, etc.
The ECU 51 further includes an external input circuit 57 and an external output circuit 58, which constitute, together with the above elements 52 through 56 and a bus 59 connecting them with one another, a logical operation circuit.
The ROM 53 stores in advance programs related to a variety of driving control, trouble diagnosis, etc, and the RAM 54 temporarily stores the results of logical operations or the like of the CPU 52.
The backup RAM 55 is a nonvolatile RAM which is backed up by a battery for preserving written data even when the ECU 51 is non-active or deenergized (i.e., when the power supply is off).
The timer counter 56 is capable of performing a plurality of counting operations at the same time.
The external input circuit 57 includes a buffer, a filter, an analog to digital converter, a drive circuit, etc.
A throttle sensor 42 detects the opening degree of a throttle valve corresponding to the amount of depression of an accelerator pedal (not shown) by the driver. A rotation sensor 43 detects the rotational speed of the crankshaft 5, that is, the number of revolutions per minute of the engine.
An oxygen sensor 44 detects the density of oxygen in the engine exhaust gas and an intake air pressure sensor 45 detects the intake air pressure (the pressure of intake air), and a vehicle speed sensor 46 detects the running speed of a vehicle. An intake air temperature sensor 47 detects the temperature of intake air (intake air temperature) introduced into an air cleaner (not shown) provided at an inlet end of the intake pipe.
These various sensors 41 through 47 are connected with the external input circuit 57 in the ECU 51 so that the CPU 52 reads in the detection signals of the various sensors 41 though 47 input thereto through the external input circuit 57 as input values.
For instance, the CPU 52 performs various driving control operations such as control of the fuel injection amounts and the fuel injection timing of fuel injectors 48, and trouble diagnosis of the thermostats 16, etc., based on the input values.
The ECU 51 further includes a heat amount parameter detection section for detecting a predetermined operating condition related to the amount of heat generated bey the engine 1 as a heat amount parameter, and an abnormality determination section for determining the presence or absence of abnormality of the thermostat 16 based on the heat amount parameter.
The abnormality determination section in the ECU 51 determines the presence of abnormality in the thermostat 16 (e.g., oversupply of cooling water to the radiator 8) if the temperature TW of cooling water does not reach a predetermined allowable lower limit when the heat amount parameter reaches a reference heat amount after the engine 1 has been started.
In this manner, a determination of abnormality in the thermostat 16 can be made by determining the presence or absence of the cooling action (circulation of cooling water) for a predetermined period of time based on the amount of heat generated by the engine 1 (i.e., the amount of heat for heating cooling water), which is a factor of the rising temperature TW of cooling water.
Particularly, when the warming up of the engine 1 is delayed due to the abnormality of the thermostat 16 (e.g., excessive supply of cooling water to the radiator 8), the combustion state is deteriorated to degrade the components of the exhaust gas at the cold starting of the engine 1, and hence it is necessary to promptly detect abnormality in the thermostat 16 and repair the failure thereof.
Next, reference will be made in more detail to an operation of the ECU 51 for detecting abnormality in the thermostat 16.
First of all, in order to initially set the temperature TWs of cooling water an allowable lower limit (abnormality determination value) T1, etc., the ECU 51 determines, based on an electric signal from a starter switch (not shown), whether the engine 1 is in a starting period (initial state)
When the engine is being started, the ECU 51 reads in the current temperature TW of cooling water based on the detection value from the water temperature sensor 41, and sets the current temperature TW of cooling water as an initial value TWs of the temperature of cooling water (i.e., cooling water temperature at the engine starting).
Thereafter, a reference value (reference heat amount) EQo for determining whether to execute the abnormality detection of the thermostat 16 is calculated from the temperature TWs of cooling water at the starting of the engine 1 based on a map (not shown) stored in the ROM 53.
At this time, the map is formulated in such a manner that the reference heat amount EQo becomes smaller as the cooling water temperature TWs at the starting of the engine 1 is higher. This is because the temperature TW of cooling water rises easily up to a predetermined temperature due to a smaller amount of heat supply if the starting time or initial cooling water temperature TWs is high.
Subsequently, an estimated amount of temperature rise ΔT is calculated by referring to the map based on the starting time (initial) temperature TWs of cooling water.
Here, note that the estimated amount of temperature rise a ΔT represents an estimated amount of temperature rise of the cooling water temperature TW occurring when there is generated a predetermined amount of heat by the engine 1.
Moreover, the relation of the estimated amount of temperature rise ΔT to the starting time cooling water temperature TWs is similar to the relation of the reference heat amount EQo to the starting time cooling water temperature TWs.
After the estimated amount of temperature rise ΔT is added to the starting time cooling water temperature TW's to provide an allowable lower limit T1, which is then temporarily stored in the RAM 54, the ECU 51 determines a proper allowable lower limit T1 suitable for the abnormality detection of the thermostat 16 based on the starting time cooling water temperature TWs.
On the other hand, when the engine 1 is not in a starting period, the latest value of the estimated amount of heat (corresponding to the estimated amount of temperature rise ΔT), which is to be updated upon each fuel injection, is read in, and if this latest value meets the requirement that it is equal to or greater than the reference heat amount EQo, a determination is made as to whether the current temperature TW of cooling water is not less than the allowable lower limit T1.
When TW≧T1, it is determined that the thermostat 16 is in a normal state, whereas when TW<T1, it is determined that the thermostat 16 is in an abnormal state.
In this manner, in the known apparatus illustrated in FIG. 12 and FIG. 13, when the parameter related to the amount of heat generated by the engine 1 (the estimated amount of heat corresponding to the estimated amount of temperature rise ΔT) reaches the reference heat amount EQo, the temperature TW of cooling water is compared with the preset allowable lower limit T1, so that when the temperature TW of cooling water has not yet reached the allowable lower limit T1, it is determined that there is abnormality in the thermostat 16.
Here, the heat amount parameter is an integrated value of the amount of heat generated by the engine (i.e., the amount of heat given to the cooling water), which is estimated from the amount of intake air, etc., related to the combustion of the engine 1.
Accordingly, in the case where the amount of heat generated by the engine per unit time is limited (for instance, during idling operation), the time required until the heat amount parameter reaches the reference heat amount becomes extremely long.
That is, in the case of a small amount of heat generated such as during idling, etc., the time required until the heat amount parameter reaches the reference heat amount becomes long, and hence a long time is required for abnormality determination of the thermostat 16, thus reducing the number of times of abnormality determinations.
In addition, even if the integrated value corrected by the air fuel ratio A/F of a mixture, the vehicle speed, the intake air temperature, etc., is used as the heat amount parameter in order to calculate the amount of heat generated by the engine with high accuracy, abnormality determination at the time of idling operation in which the abnormality determination time becomes longer will be remarkably affected by radiational cooling according to road conditions (frozen road, etc) around the vehicle, and the influence of cooling of the engine 1 due to rain water during traveling in rainy weather.
Therefore, it becomes difficult to accurately estimate the amount of heat (i.e., the amount of heat generated by the engine) given to the cooling water, and hence there is a fear that it might be mistakenly determined that the thermostat 16 is in an abnormal state in spite of the thermostat 16 being actually normal.
On the other hand, the heat amount parameter is an integrated value of the amount of heat generated by the engine estimated from the amount of intake air, etc., so in cases where there is a lot of heat generated per unit time by the engine (for instance, during climbing up a slope, running on a snowy road, etc.), the time required until the heat amount parameter reaches the reference heat amount becomes extremely short.
Moreover, in such a case of traveling with a large amount of heat generation, most of the heat generated by the engine contributes to increasing the temperature TW of cooling water, and hence the cooling water temperature WT rises irrespective of the presence or absence of abnormality in the thermostat 16, whereby it might be incorrectly determined that the thermostat 16 is in a normal state, though the thermostat 16 is in actuality abnormal.
Since the known abnormality detection apparatus of an engine temperature adjusting thermostat calculates the integrated value of the amount of heat generated by the engine as the heat amount parameter, as described above, in cases where the amount of heat generation per unit time is limited such as at the time of idling operation, etc., it takes a long time until the heat amount parameter reaches the reference heat amount, and hence it is easily affected by the cooling condition of the engine. As a result, it becomes difficult to accurately estimate the amount of heat generated by the engine, giving rise to a problem that an incorrect determination of the thermostat 16 being abnormal is made in spite of the fact that the thermostat 16 is actually normal.
In contrast, in cases where the amount of heat per unit time generated by the engine is great, the time required until the heat amount parameter reaches the reference heat amount becomes extremely short, and hence most of the heat generated by the engine contributes to raising the temperature of cooling water. As a result, the temperature of cooling water rises similarly regardless of the abnormality or normality of the thermostat 16, and hence there arises another problem that an incorrect determination is made that the thermostat 16 is normal though the thermostat 16 is actually abnormal.